1. Field of the Invention
This invention generally relates to communication systems and, more particularly, to a system and method for negotiating a link rate in a communication system where link partners are optionally capable of transceiving at two or more data rates, on one or more physical medium lanes.
2. Description of the Related Art
FIG. 1 is an auto-negotiation and training state diagram for an IEEE 802.3ap compliant network (prior art). The diagram is a state machine demonstrating the steps in an auto-negotiation (AN) process between boards across a backplane. Devices in such a backplane may be capable of operating at 1 gigabits per second (1 G), 10 G, and both 1 G and 10 G. Further, some units are able to send AN pages, compliant with Clause 73 of 802.3ap, to negotiate a data rate. Following power-up, reset, link fault, or time-out (100) the driver is disabled for a pre-determined period of time, which forces the link partner to restart. Next, the driver sends AN pages and the receiver looks for AN pages (102). If AN pages are detected, then the rate is negotiated based on local and received abilities.
If AN pages are not detected, then the Rx looks for a 1 G signal (104). If a 1 G signal is detected or negotiated, then the data path is configured for 1 G and 1 G acquisition begins (106). If 1 G cannot be detected, the receiver looks for a 10 G signal. If 10 G is negotiated, then the data path is configured for 10 G training and 10 G training begins (110). When 1 G acquisition or 10 G training is complete, the data path is configured for 1 G or 10 G, tracking and data transmission may begin at steps 108 and 112, respectively. If 10 G training does not complete within 500 ms, or if 1 G acquisition does not complete within 50 ms, or if a fault is detected while training, tracking, or acquiring, AN will restart (100).
Devices in a backplane may also be connected through more than one physical medium lane. As used herein, a physical medium lane is a physical medium, such as a cable or optical fiber. In some aspects, the link between two devices may be composed on multiple lanes. As an example, XAUI is a four-lane interface with a 3.125 Gbps baud rate or 2.5 Gbps data rate per lane with an aggregate data rate of 10 Gbps. For various reasons, such as backward compatibility or to manage power consumption, it may be necessary or desirable to operate at either the maximum rate of 10 Gbps, or a lower rate of 1 Gbps. For example, on a conventional XAUI backplane interface, it is common to have option of 1 Gbps on lane 0, with other lanes disabled when 1 Gbps rate is desired. In order for the links to run at a common rate, a common negotiation method is required.
It would be advantageous if a streamlined process of AN were developed that could account for devices capable of AN, dual-rate devices without AN capacity, single-rate devices, and multilane devices.